A stent is commonly used as a tubular structure left inside the lumen of a duct to relieve an obstruction. Commonly, stents are inserted into the lumen in a non expanded form and are then expanded autonomously (or with the aid of a second device in situ. A typical method of expansion occurs through the use of a catheter mounted angioplasty balloon which is inflated within the stenosed vessel or body passageway in order to shear and disrupt the obstructions a associated with the wall components of the vessel and to obtain an enlarged lumen.
In the absence of a sent, restenosis may occur as a result of elastic recoil of the stenotic lesion. Although a number of stent designs have been reported, these designs have suffered from a number of limitations. These include restrictions on the dimension of the scent such as describes a stent which has rigid ends (8 mm) and a flexible median part of 7-21 mm. This device is formed of multiple parts and is not continuously flexible along the longitudinal axis. Other stent designs with rigid segments and flexible segments have also been described.
Other stents are described as longitudinally flexible but consist of a plurality of cylindrical elements connected by flexible members. This design has at least one important disadvantage, for example, according to this design, protruding edges occur when the stent is flexed around a curve raising the possibility of inadvertent retention of the stent on plaque deposited on arterial walls. This may cause the stent to embolize or more out of position and further cause damage to the interior lining of healthy vessels. (See FIG. 1(a) below).
Thus, stents known in the art, which may be expanded by balloon angioplasty, generally compromise axial flexibility to permit expansion and provide overall structural integrity.
Catheter balloons and medical devices incorporating them are well known for use in the surgical arena. For instance, during angioplasty, stenoses and/or obstructions in blood vessels and other body passageways are altered, in order to increase blood flow through the obstructed area of the blood vessel. For example, in a typical balloon angioplasty procedure, a partially occluded lumen is enlarged through the use of a balloon catheter that is passed percutaneously by way of the arterial system by way to the site of the vascular obstruction. The balloon is then deflated to dilate the vessel lumen at the site of the obstruction.
Furthermore, another typical procedure uses a "scaffolding," or stent placed on the balloon angioplasty catheter for similar delivery through the arterial system to the site of a vascular obstruction. Thereafter, the balloon angioplasty catheter is inflated, thereby expanding the stent placed on the catheter. When the stent expands, it similarly expands the lumen so that after removal of the deflated catheter, the stent is retained in its expanded position and thereby holds open that formerly obstructed area of the body passageway.
Essentially, a balloon catheter is a thin, flexible length of tubing having a small inflatable balloon at a desired location along its length such as at or near its tip. Balloon catheters are designed to be inserted into a body passageway such as the lumen of a blood vessel, a passageway in the heart, a urological passageway, and the like. Typically, the passage of the balloon catheter into the body passageway is done with guidance, such as x-ray or fluoroscopic guidance.
In practice, stent delivery is quite complex. That is, a stent is sometimes required to be placed in a rather tortuous area of the vasculature. In this instance, it is often necessary to have a catheter which is capable of negotiating tight turns, and/or being placed along a bifurcated length of blood vessel. In some instances, while a generally occluded section of blood vessel can readily be stented, it is often difficult to place a second stent at the other portion of a bifurcation. In other words, one can imagine the bifurcation as an inverted letter "Y" within the body. (The approach of the catheter concerning this inverted "Y" shape is generally through one of the legs in the "Y".) Therefore, the balloon passes both between the leg and the trunk or base of the "Y" rather readily. However, once a stent is placed along these two legs, it is rather difficult to place a second stent at or near the junction of the first leg and the base of the letter "Y". Of course, the same can hold true when the approach is via the base of the "Y" and delivery of the first stent is to one of the legs. This is all the more true because as one advances through the vasculature, the arterial sizes go from quite large (greater than 1 cm diameter) to rather small (some time less than 2.5 mm diameter).
It would be desirable, therefore, to create a system which allows for delivery of a single stent or pair of stents at a bifurcation in the vasculature. It would further be desirable for this stent or for this delivery system to be able to negotiate the bends of the bifurcation, and moreover, to provide for easy access when one stent is already placed. Furthermore, it would be quite useful in order to be able to apply the second stent, for the first stent to be reliably placed every time so that the user knows exactly where the bifurcation is located, and as well where the stent must be appropriately oriented in order to readily access the second leg of the "Y" of the bifurcation.
Finally, it would be useful for a device such as a desired delivery system to carry a stent capable of allowing secondary access to a bifurcated portion of the vasculature. Thus, it would be most desirable for the device to comprise a catheter capable of balloon delivery of a stent at a bifurcation, and also balloon delivery of a second stent at the bifurcation.